Change ArborX hash to "hash-dirty" if worktree is not clean

[aprokop]

If a tree is dirty, it will print <hash>-dirty. This is helpful when we share logs.

One caveat is that if the HEAD points to an annotated tag, it will print a tag instead of a hash. However, I think we are only using lightweight tags, so I don't see much of an issue, and feel like it's worth doing this.

[dalg24]

Did you look how other projects deal with this?
For instance https://github.com/google/benchmark/blob/main/cmake/GetGitVersion.cmake which seems to be used in llvm-project as well.

I don't think it is an issue to use a tag when it exists.

[aprokop]

I chose the path of least effort to improve status quo. It was not my intent to provide the final solution to the problem, which your reference may be.

I don't think it is an issue to use a tag when it exists.

The only concern I have about this is that tags maybe removed and readded, and correspond to different hashes. If we promise not to do that, it is not a concern. Or we can promise not to add annotated tags, in which case it's always a hash.

[aprokop]

Opted in favor of rev-parse and status -porcelain. This should be robust.
I'm not sure if the code in benchmark's git cmake brings any benefit to this:

      # Work out if the repository is dirty
      execute_process(COMMAND ${GIT_EXECUTABLE} update-index -q --refresh
          WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
          OUTPUT_QUIET
          ERROR_QUIET)
      execute_process(COMMAND ${GIT_EXECUTABLE} diff-index --name-only HEAD --
          WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
          OUTPUT_VARIABLE GIT_DIFF_INDEX
          ERROR_QUIET)
      string(COMPARE NOTEQUAL "${GIT_DIFF_INDEX}" "" GIT_DIRTY)
      if (${GIT_DIRTY})
          set(GIT_DESCRIBE_VERSION "${GIT_DESCRIBE_VERSION}-dirty")
      endif()

[dalg24]

Fine by me. I only have a minor comment.

[aprokop]

@dalg24 Changed to --untracked-files=no.